1. Field of the Invention
The present invention relates to a water jet propeller apparatus for a vessel, such as a personal watercraft. More particularly, the present invention relates to a water jet-propeller apparatus in which an impeller and an impeller shaft are joined in a manner such that water intrusion via the impeller shaft is minimized, and a corrosive effect on the impeller shaft is reduced, due to its limited exposure to the water being propelled by the impeller.
2. Description of the Background Art
A small waterboat, or personal watercraft, is a small size craft that is constructed and arranged to glide under power across the surface of a sea or of a lake. Many jet skis and other different types of personal watercraft are known and are commercially available.
In the art relating to personal watercraft, some designs for water jet propellers are known. For example, FIG. 6 hereof is a reproduction of one of the drawings from Japanese utility Model Registration No. 2548210. FIG. 6 is included herein for purposes of discussing one example of a previous design for a water jet propeller.
The known water jet propeller apparatus of FIG. 6 is mounted to the rear portion of a vessel body. The known water jet propeller apparatus of FIG. 6 includes a stator (duct) 1 defining a channel, an impeller 2 rotatably disposed inside the stator channel, and an impeller shaft 3, connected to the back of the impeller 2, and rotatably supported by a bearing unit 1a in the stator 1. The water jet propeller apparatus of FIG. 6 also includes a collar 4, provided on the outer periphery of the impeller shaft 3, and a water-resistant seal 5 provided between the collar 4 and the bearing unit 1a. A drive shaft 6 is connected to the front of the impeller 2, and the impeller 2 is rotated via the drive shaft 6 which, in turn, is driven by an engine (not shown). The vessel body is propelled by ejection of water toward the rear (to the right in the drawing).
In the jet propeller in the reference described above, a front edge 4a of the collar 4 simply and abuts against a rear edge 2a of the impeller 2 in a non-sealed manner. There is a problem with the design of this reference, in that water may leak in through a gap between the front edge 4a of the collar 4 and the rear edge 2a of the impeller 2. After leaking through the aforementioned gap, such water may come into contact with the surface of the impeller shaft 3, thereby undesirably corroding the surface of the impeller shaft 3.
This problem can be minimized by forming the impeller shaft 3 out of a corrosion-inhibiting material (for example, stainless steel). However, cost of this corrosion-inhibiting material can be prohibitive.
Although the known devices have some utility for their intended purposes, a need still exists in the art for an improved water jet propeller apparatus for a personal watercraft. In particular, there is a need for an improved water jet propeller apparatus in which an impeller and an impeller shaft are joined in a manner such that water intrusion via the impeller shaft is minimized.